1. Field of the Invention
The present invention relates to a cleaning blade for use in an image forming apparatus such as an electrophotographic copier, a printer, a facsimile apparatus or the like, and more particularly to a cleaning blade to be maintained in contact with the surface of an image bearing member to be cleaned thereby removing the toner remaining on said surface, and a producing method therefor.
2. Related Background Art
In an image forming apparatus designed to repeat a process of transferring a toner image, formed on the surface of an image bearing member, onto a transfer material such as paper, it is desirable to completely eliminate the untransferred toner remaining on said member after each transfer process, in order to prevent the smearing of the image by the remaining or residual toner at the next transfer process. For this purpose there is widely employed so-called blade cleaning method in which an edge of high precision formed with rubber elastomer is maintained in uniform contact with the surface of the image bearing member to slide on said member, thereby removing the toner remaining thereon. Said rubber elastomer is generally composed of urethane rubber, and thermosetting liquid urethanes are particularly preferred in consideration of the superior abrasion resistance thereof.
However, the cleaning blade composed of urethane rubber generates, because of a high friction coefficient of the urethane rubber, a very high friction force between the blade and the image bearing member in the initial stage of sliding motion when the toner is absent therebetween. Consequently the cleaning blade of urethane rubber may be inverted as indicated by broken lines in FIG. 3 or may bounce on the image bearing member in the initial stage of sliding motion, thereby becoming unable to remove the remaining toner.
In consideration of such situation, there has been proposed and employed a method of reducing the frictional force between the urethane rubber and the image bearing member in the initial stage of the sliding motion, by coating the end portion of the cleaning blade of urethane rubber or the surface of the image bearing member with lubricating powder of fluorinated resin such as polyvinylidene fluoride (PVDF) or polytetrafluoroethylene (PTFE) (hereinafter represented as "lubricant"). However, excessive use of such lubricant may result in smearing of the developing unit or the charging unit, or may deteriorate the image quality because of its electrical properties. It is therefore necessary to obtain uniform coating with a minimum possible amount, but such coating is technically difficult to realize and the obtained blade cannot be fully reliable with respect to the blade inversion or bouncing, due for example to fluctuation in the coating.
In order to resolve this drawback, the Japanese Laid-open Patent No. 61-48881 proposes to disperse the lubricant in the urethane rubber material. However, in a simple dispersion system, the lubricant only locally appears on the surface as shown in FIG. 4, and the inversion or bouncing of the blade cannot be completely prevented as the urethane rubber used as the matrix considerably influences the behavior. Besides the thermosetting liquid urethanes are unsuitable for mass production, since they require a long reaction time for thermosetting and have high reactivity with moisture in the air.
On the other hand, a rubber material of low friction resistance and short reaction time, for example silicon rubber with satisfactory stability in ambient conditions, is effective for preventing the blade inversion or bouncing and is suitable for mass production. However silicon rubber is easily abraded and cannot be used for a long time, since the blade edge is abraded by the friction with the image bearing member or with the toner.